Resistor



Dec. 13, 1966 R. A. ROQUES 3,292,130

RESISTOR Filed July 28, 1961 2 Sheets-Sheet l TEMPERATURE IN DEGREES CENTIGRADE 3 700 500 I00 0 50 |00 l50 I I I I I I I INTRINSIC CONDUCTION RESISTIVITY IN OHM CENTIMETERS INVENTOR Rodney A. Roques ATTORNEYS Dec. 13, 1966 R. A. ROQUES 3,292,130 I RESISTOR Filed July 28, 1961 2 Sheets-Sheet 2 F|G.2. K w 44 35 m 45 v 32 33 34 g He* 38 o Q. T DJ H ELECTRIC POWER SUPPLY FIG. 3.

INVENTOR Rodney A. Roques ATTORNEYS United States Patent 3,292,130 RESISTOR Rodney A. Roques, Richardson, Tex., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed July 28, 1961, Ser. No. 127,691 Claims. (Cl. 338308) This invention relates to a method of fabricating film resistors and to resistors produced by the use of the method.

Since the advent of the transistor and other semiconductor elements, great progress has been made in minia turizing electrical components to reduce their cost by an economy of materials and to reduce their size to conserve space. As one such component, the resistor has undergone considerable development in this direction, particularly resistors of the film type in which a film of metal or carbon is deposited on an insulating support to form the resistor.

One object of this invention is a film resistor of which the film is a semiconductor material suitably doped with conductivity determining impurities, the thickness of the film and the amount of impurity therein being controllable to impart some or all of the properties required of a resistor, for example, desirable temperature coefficient of resistance, absolute resistance, close tolerances and high or low resistivity.

Another object of the invention is a method by which such a resistor may be produced.

'Other objects, advantages and features of this invention will become apparent from the following detailed description, taken in conjunction with the appended claims and the accompanying drawings, in which:

FIGURE 1 is a graphical representation of the electrical resistivity of boron doped silicon for several boron concentrations, plotted against temperature;

FIGURE 2 is a schematic flow diagram of an apparatus illustrating one method for depositing a thin film of a semiconductor material on an insulating support; and

FIGURE 3 is a sectional view of a reaction furnace used in the practice of making one embodiment of the present invention.

Referring to FIGURE 1 of the drawings, there is shown on a logarithmic scale the electrical resistivity of silicon doped boron for several boron concentrations, plotted against temperature. Numeral 16 rep-resents the locus at which the electrical conduction of silicon becomes intrinsic for various boron concentrations. (Intrinsic conduction for a semiconductor is defined, for purposes of this application, to be the electrical conduction of the semiconductor that is due primarily to the inherent properties there-of. This state of conduction is usually attained by heating the semiconductor to a temperature of which further increase thereof has the effect of increasing the electrical conductivity of the semiconductor by exciting electrons in the atoms comprising the crystal lattice from the valence band to the conduction band.) Numeral 2 represents the temperature versus resistivity curve of silicon containing about boron atoms per cubic centimeter. In contrast with this is the temperature versus resistivity curve 10- of silicon that contains about 10 boron atoms per cubic centimeter, the silicon having a sufiicient density of boron atoms therein to cause the silicon to approach a condition whereby a further addition of impurities has little or no effect on the electrical conduction of the sample. It may be noted from curve 10 that the electrical resistivity of silicon approaches a minimum variation with temperature as the silicon approaches this condition. Thus it is advantageous to utilize silicon having a high density of boron atoms to achieve a low temperature coefiicient of resistance.

Semiconductors other than silicon may be chosen for the production of film resistors since the general tenor of thQCUI'VCS shown in the FIGURE 1 is characteristic of most semiconductors, for example,. germanium, indium antimonide, etc. Moreover, impurities other than boron, both pand n-type, have the same effect in semiconductors for the purposes of the present invention.

To provide a resistor having the aforementioned advantages, a thin film of silicon of predetermined thickness is deposited on a suitable insulating member such as ceramic or glass. Spaced apart electrical contacts are made to the resistance film to complete the device.

Any one of several methods may be used to deposit films on insulating members. For example, an amount of silicon containing an appropriate amount of impurities can be evaporated onto an insulating plate. As a preferred method, however, pyrolytically depositing silicon onto an insulating member from a silicon halide in the presence of hydrogen gives very desirable results. The film thickness can be adjusted to whatever value desired, the impurities being added to the silicon film during the depositing thereof.

FIGURE 2 diagrammatically illustrates an apparatus for pyrolytically depositing a silicon film, containing an appropriate amount of impurities therein, on an insulating plate. A valve 39 allows hydrogen to pass from inlet 40 to an evaporation chamber 38. A source 30 of liquid silicon tetrachloride (SiCl mixed with liquid boron tribr-omide (BBr is contained in vessel 31. A flow of inert gas, such as helium, into vessel 31 is provided by a source 32 through valve 33. An outlet 34 and valve 35 provide for the mixture of SiCl and BBr to pass from the vessel 31 to evaporator 38. Hydrogen, flowing through evaporation chamber 38, totally evaporates the mixture of SiCl and BBr present in the evaporator 38. A flow line 42 allows the evaporated SiCl -BBr mixture and hydrogen to pass into a quartz reaction furnace 54. An excess pressure line 44 and valve 45 are provided in flow line 42. A vent 62 is provided at one end of furnace 52 to remove excess gasses.

As one example for pyrolytically depositing a silicon film on an insulating plate, a 96% alumina ceramic plate 57, manufactured by the American Lava Company and having dimensions of 1 inch by 0.5 inch by 0.01 inch, is placed on a carbon filament heater 56 within the quartz reaction tube 54, as shown in FIGURE 2. The ceramic plate 57 is heated to about 1050 C. by an electric current passing through the carbon heater 56, the electric current being provided by power supply 74 through wires 72. The Wires 72 are passed through the walls of the quartz tube 54 by any suitable means, such as the hermetic seal 70.

Hydrogen, flowing at a rate of about 4.8 liters per minute, is passed through evaporator 38, flow line 42, and into the reaction furnace 54. The hydrogen is passed over the heated ceramic plate for about 3 to 5 minutes to clean its surface, the hydrogen passing out through vent 62. During this time valve 35 remains closed so that only hydrogen enters the reaction furnace 54. After the cleaning process is completed, valve 35 is opened to permit a flow of the SiCl -BBr mixture into the evaporator 38. This flow is accomplished by maintaining a suitable pressure of inert gas, such as helium, from source 32 through valve 33 into the vessel 31.

A solution of 0.27 percent by volume of BB in SiCl, is passed into evaporator 38 by flow line 34 and valve 35 at a rate of about 1.6 cubic centimeters per minute. Hydrogen, flowing at the above-noted rate of about 4.8 liters per minute, totally evaporates the SiCl -BBr mixture and carries the mixture through flow line 42 into reaction chamber 54 where it passes over the surface of the heated ceramic plate 57. The SiCl -BBr mixture,

passed over the ceramic plate A thin film 58 of silicon, containing boron as an impurity, is thereby deposited thereon.

carried by the hydrogen, is 57 for about 15 minutes.

TABLE 11 After the deposition is completed, the SiCL -BBr mixture is turned off by valve 35, and the temperature of the silicon Carbon Metal ceramic plate is gradually reduced to room temperature 1 in the Presence of the flowing hydrogen y l'edllcmg the Specific Electrical Resistivity 1& to 10 to 10- 1w to 10- electric current through the carbon filament by about 5 S g q percent of the maximum current every minute. The 1 105 101150 4 i 3 gradual reduction of the temperature prevents thermal 10 Film Thickness 10 M110 10 m 10 10 mm Temperature Coeificient stresses from breaking the film and ceramic plate 5 S (p,p.m./ o. 125F100 200-500 25-50 a result of the foregoing process, a film of thickness of about 0.4 mil is deposited on the ceramic plate. The silicon film, deposited according to the foregoing process, is Table 2 l 9 coefiiclelits of DIS/crystalline is of very fine grain is Smooth and is sistanceo t esilicon mresistors of the present invention 5 Well bonded to the ceramic late are as low, or lower, than those of carbon film resistors y P While the specific electrical resistivities of the silicon film It Should be noted that the foregomg pyrolytlc Process resistors are as .hi h as those of carbon film resistors for providing a thin semiconductor film on an insulating ban much hi ,[han those for metal fihm resistors plate has many advantages some of which are the fol' The thickness if the silicon films can be made much lpwmg' The prqcess adaptable any .Semlconductor greater than those of either the carbon or metal film rematerial and any impurity comblned therewlth. The temsistors and yet attain as high a resistivity and as low a i g g 125;: fi i g; 3 Z EZE E E EE FS SS Z temperature coefiic-ient of resistance as those for a carbon i i be used to rovide a film of 6 i thickness film. This means that fabrication yields, percentage-wise, Th do m.xture b a Se 25 are much greater for silicon film resistors than for either z gi regctiorn 5 31 3 54 a g; 5 carbon or metal film resistors since irregularities of either the insulating support surface or resistance films do not time, thus providing a correspondingly thlcker or e as appreciably aiTect the ultimate resistance of the film. film 58. A greater or lesser percent by volume, or Weight, Insulating Supports other than flat plates can be used of impuriiy.may be aimed the Semic0nduc.t()r mixture as the depositing support for the resistance films. For 3 fif i f z g g ggfi gg i z gg example cylindrical insulating cores (either hollow or p g y g SOlld) can be suspended in the reaction furnace by a metal variables thus enhance the process of ad usting the ulti- Wire passing through a hole in the core AS shown in mate characteristics of the resistors as desired. FIGURE 3 a hollow Ceramic core i Suspended by The characteristics of five resistance films made accorda wire 102 Smmg from Supports 104 The assembly is ing to the foregoing PYPCBSS are Shown in Table The placed in the quartz tube 106 which is surrounded by function surface resistlvity in ohms per l i is used the cylindrical furnace 108. An electrical current passes as a quantitative measure of the electrical resistivity Where through wire Winding 110 of the furnace 108 to heat the the tgickness 01f1 the film cannot easily be measured, and core 100 within the quartz tube 106. The method for 15 de ned as f0 depositing a resistance film on the surface of the ceramic R= L/ core 100 is the same as described in connection with the t=thickness of the film, ceramic plate 57 of FIGURE 2. After the resistor eleid h f th film, ment has been produced according to the foregoing meth- L=length of the film, 0d, suitablespaced-apart electrical terminals (not shown) =spccific l t i l resistivity of th fil d for connecting the resistor as a component of an electric R=total resistance of a film of length L and an area wt. clrcult, y attached to the re$1tahe layer y y 0f Th the Well known methods available in the art.

Although a silicon film containing boron as an impurity R (boron being a p-type conductivity impurity in semip/t L/ reslsnvlty m ohms per Square conductors) has been described as a specific embodiment TABLE I Approximate /tin Temperature (Calcu- Film thickness L, in w, in Ohms/ Coefficient lated) R, in

t,inMi1 Inches Inches square of Resistance in Ohms inp.p.m./ C. Ohm-cm.

I 0.4 1 0.5 0.071 II 0.4 1 0.6 45 180 0. 046 90 III.-- 0. 4 1 0. 5 90 240 0. 091 180 IV- From Table I, it may be seen that silicon films can be of this invention, other impurities, either por n-type, produced with a very low temperature coefiicient of re- 65 may be used in silicon. Moreover, reference to a graphsistance and a fairly high specific electrical resistivity. ical representation of the electrical resistivity of germani- If the temperature coefficient of resistance is allowed to um as a function of temperature for different impurity increase by reducing the density of impurities in the concentrations shows that excellent film resistors can be silicon, a much higher specific electrical resistivity can be made by pyrolytic-ally depositing germanium on electrical achieved. By controlling the density of impurity in the 70 insulating members. In fact, the present invention is apsilicon, a resistor can be made that has a low temperature plicable to any semiconductor exhibting similar charactercoefficient of resistance and a higher specific electrical istics as shown for silicon in FIGURE 1 of the drawing. resistivity. Insulating supports of many sizes and shapes may be To illustrate how silicon film resistors compare to carused as the depositing surface for the resistance films. bon and metal film resistors, reference is made to Table II 75 Although a ceramic insulating support is used in the deshowing the ranges of specific electrical resistivity, surface tailed description of the invention, glass will equally suf- 5 fice as the insulating support, as will other suitable insulating materials. Thus the invention is intended to be limited only by the appended claims.

What is claimed is:

1. A resistance element comprising an electrical insulating member, a film of silicon deposited on said member, said silicon containing about 10 to about 10 conductivity determining impurity atoms per cubic centimeter, and spaced apart electrical connections to said film.

2. The resistance element as defined in claim 1 wherein said impurity atoms are boron.

3. A resistance element comprising an electrical insulating member selected from the group consisting of ceramic and glass, a film of silicon deposited on said member, said silicon containing about 10 to about 10 boron atoms per cub-ic centimeter, and spaced apart electrical connections to said film.

4. A resistance element comprising an electrical insulating member, a film of silicon semiconductor material deposited on said member, said material containing a sufficient concentration of a conductivity determining impurity to impart a substantially maximum conduction References Cited by the Examiner UNITED STATES PATENTS 2,778,743 1/1957 Bowman 117-46 2,784,121 3/1957 Fuller 148-189 2,920,006 1/1960 Yutema et a1 117-106 X 2,934,736 4/1960 Davis 338-308 2,935,717 5/1960 Solow 338-308 2,959,499 11/ 1960 Herczog et a1 117-229 2,961,352 11/1960 Grattidge et al 117-229 2,986,481 5/1961 Gudmundsen 148-179 3,009,840 11/1961 Emeis 148-179 3,137,597 6/1964 Patalong et a1. 148-185 X 20 RICHARD M. WOOD, Primary Examiner.

RAY K. WI'NDHAM, Examiner.

H. T. POWELL, V. Y. MAYEWSKY,

Assistant Examiners. 

1. A RESISTANCE ELEMENT COMPRISING AN ELECTRICAL INSULATING MEMBER, A FILM OF SILICON DEPOSITED ON SAID MEMBER, SAID SILICON CONTAINING ABOUT 10**18 TO ABOUT 10**20 CONDUCTIVITY DETERMINING IMPURITY ATOMS PER CUBIC CENTIMETER, AND SPACED APART ELECTRICAL CONNECTIONS TO SAID FILM. 